1. Field of the Invention
The present invention relates to a method for lubricating a compression-type refrigerating cycle. More particularly it relates to a method for lubricating a compression-type refrigerating cycle efficiently without detracting wear resistance, cooling effect and stability by employing a specific lubricant in combination with a refrigerant comprising substitute fluorohydrocarbon (hereinafter referred sometimes to as "flon compound") such as 1,1,1,2-tetrafluoroethane (R-134a).
2. Description of the Related Arts
Conventionally, in a compression-type refrigerating cycle comprising a compressor, a condenser, an expansion valve and an evaporator, a flon compound including a fluorinated hydrocarbon such as dichlorodifluoromethane (R-12) and chlorodifluoromethane (R-22) has been used as the refrigerant. Many lubricants compatible with them has also been made industrially available for use.
However, there have been misgivings that these flon compounds widely used as the refrigerant are liable to cause depletion of the ozone layer and environmental pollution after they are released into the open air. In an effort to prevent environmental pollution, fluorohydrocarbons (or chlorofluorohydrocarbons), for example 1,1,5,2-tetrafluoroethane (R-134a) and the like, have been developed as a possible replacement in recent years. Until now there have been introduced into market many so-called substitute flon compounds with minimized danger of environmental pollution and capable of satisfying said required properties, for example 1,1,2,2-tetrafluoroethane (R-134) and the like, as well as R-134a. These new substitute flon refrigerants are different from conventional flon refrigerants in characteristics. Thus, glycol compounds, ester compounds and the like have been proposed as the lubricant for use in combination with them (U.S. Pat. No. 4,755,316 and Japanese Patent Laid Open No. 33193/1991), but their wear resistance, cooling effect and stability have not been found satisfactory to a full extent.